806

(1)

IS:806-1988

Indian Standard

CODE OF PRACTICE FOR

USE OF STEEL TUBES IN GENERAL

BUILDING CONSTRUCTION

(First Revision)

Eleventh Reprint JUNE 1996

( Incorporating Amendment No. 1 )

UDC 669.14.018.29-462 : 69

8 Copyright 1973

BUREAU

OF INDIAN

STANDARDS

MANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG NEW DELHI 110002

Gr5

February 1968

(2)

Indian Standard

CODE OF PRACTICE FOR

USE OF STEEL TUBES IN GENERAL

BUILDING CONSTRUCTION

( First Revision)

Structural Engineering Sectional Committee, SMBDC 7

Chairrnan Representing

DIBECTORSTANDARDY( CIVIL) Ministry of Reilwnys

Members

SBRI L. N. A~RAWAL Industrial Fasteners Association of India, Calcutta

Saax M. M. M~RA~KA ( Alternate ) Sam B. D. AEUJA

SHEI P. C. JAIN ( Afternate )

Netionel Buildings Organization, New Delhi SHSI P. C. BAASIN Ministry of Transport & Communicstion [ Depert- SH~IS.R.CHAKRAVARTY

merit of Transport ( Roads Wing ) ]

Centrsl Engineering and Design Bureau, Hindu- st8n Steel Ltd, Ranchi

Sasr P. D. DHARWA~KAR ( Alternate )

SHRI D. P. CKATTERJEE Inspection Wing, Directorate General of Supplies & Disposels (Ministry of Supply, Technic81 DR P. N. CRATTEEJEI.: Government of West Bong81 Development & Materials Plannmg ) DR P. K. CHOIJDEURI Bridge & Roof CO ( Tndi8r Ltd, Howrah

SHRI A. SIEN GDPTA ( Alternate )

Dn P. DAYARATNA~

SHRI D. S. DESAI M. N. Dsstur dc Co Private Ltd, Calcutta Indian Institute of Technology, Kenpur Snsr 11. DHAR Braithwaite & Co ( India ) Ltd, Calcutta DARECTC~( DAMS)-1 Central Weter 86 Power Commission

Wing ), New Delhi SERI B. T. A. SAGAR ( AIterna?e )

(Water

SHBI M. A. D’SOUZA

SEXRI J. S. PINTO ( AIternate )

Bombay Municipal Corporation, Bombay

EXECWTIVE ENQINEER (CENTRAL Centrel Public Workr Depertment, New Delhi STORES DIVISION No. II )

f Continued on page 2 )

BUREAU OF INDIAN STANDARDS

hlANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG NEW DELHI 110002

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lS:8%-1968

( Continued from page 1 )

Members Representing

SHBI W. FEPNANDES Richardson & Cruddas Ltd, Bombay Surx P. V. NAIK ( Alternate )

SRUI P. Ssrr GUPTA Stewarts & Lloyds of India Pvt Ltd, Calcutta SRBI AI. bl. Geoelr ( Allernale )

SHIU SAILAPATX GIJPTA Public Works Department, Government of West Bengal

SHBI G. 8. IYEB Ths Hindustan Construction Co Ltd. Bombay DR 0. P. JAIN Institution of Engineers ( India ), Calcutta JOINT DIEECTOB STANDAEDS Ministry of Railways

(B&S)

DEPUTY DIRECTOR STAND-

ARDB ( B t S )-II ( Alternate )

SARI Ox KHOSLI Electrical Alanrxfecturing Ct, Ltd, Calcutta SH~I S. N. SINO~ ( Alternare )

Sent P. K. DIALLICK Burn h Co Ltd. HowraIl SHRI A. P. Kayal. ( Altrrnare )

SIIRI A. K. MITRA Hindufitan dtael Ltd, I~urgnpur &RI I~. V. HllASsAR RAO PANTuLU ( A~tertiofe I

SIIRI M. G. PAQHYE 1 rl.igaLion 9 1’0~ er Depart nbelll, G0va1 Iment of

.\ltihara?rllt.ra SunI P. V. PAwA~C ( Alrernatc)

Sttnl B. K. PANTHAKY lndhlr ltoncls Cmprsss, Xe\r Dellki

Sum U. BALWANT RAO ( Alrrrnare J

Pmv G. S. R.~HASW \MY St,ructural Engineerinr! Research C’cntra (CYIH). Roorkee

SMRI Al. iZAna!nH ( A~fer~rafe )

PBOF i). N. SAXYAL Engineer-in-Chiel’s Branch, Ministry of Vel’encc

SunI B. S. Pitanrstr RAo ( Alternare )

DB B. R. SES Indian Illntitute of Technology, Kharagpur SHEI K. V. SHETTY Central Mechanics1 Eugineering Research Ir+i-

tuto ( CSIR ), Durgspur San1 S. K. Ollosrr ( AIrrrnatP )

PROF P. K. Sobr Jadavpur University, Cnlcutta BUPR~IN~N~INO ENIJINEEII Government of Madras

( PLANNING AND DESICW

c!IllcLs j

EXECUTIVR ENGIXEER ( BUILDING CENTHE DLVISION ) ( AIrerrrate )

MAJ R. P. E. VAZIFDAB Bombay Port Trust, Bombsy

Snnr M. N. VENKATPSAN Central Water & Power Commission ( Power Wing ), New Delhi

Sam P. V. N. IYENOAR ( Alrernafe )

DB A.K. CHATTEBJBE. Director Qeneral, BIS ( Ex-officio Member )

Director ( Strut & Met )

Secretary SHRI II. S. NAOAEAJ

Assistunt Director ( Strut it Met ), BIS

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IS :

806 -

1968

Indian Standard

CODE OF PRACTICE FOR

USE OF STEEL TUBES 1N GENERAL

BUILDING CONSTRUCTION

( First Revision)

0. FOREWORD

0.1 This Indian Standard ( First Revision ) was adopted by the Indian Standards Institution on 5 January 1968, after the draft finalized by the Structural Engineering Sectional Committee had been approved by the Structural and Metals Division Council and tile Civil Engineering Divi- sion Council.

0.2 This standard is one of a series of Indian Standards being publishrd under the IS1 Steel Economy Programme. The object of this pro- qramme is to achieve economy in the use of structural steel by establish- ing rational, efficient and optimum standards for structural sections; formulation of s‘tandard codes of practice for the design and fabrication of steel structures; popularization of welding in steel construction and co-ordination and sponsoring of experimental research relating to the production and use of structural steel which would enable the formulation and revision of standard specifications and codps of practice.

0.3 This standard was first published in 1957. Since its publication foul amendments have been issued. In this revision, the following modifica- tions have been incorporated:

a) Amendments No. 1, 2, 3 and 4 have been incorporated. b) References to latest Indian Standards have been given.

c) The standard has been completely metricized.

d) Mihimum wall thicknesses of tubes have been reduced based on evidence obtained as a result of recent experimental and other investigations, subject to certain minimum maintenance conditions being observed.

0.4 This code is complementary to IS : 800-1962*. The use of tubular steel in structural work would result in considerable savings, particularly in the case of roof tlusess, latticed girders and compression mrmbers

*Code

of

prectice for use of StrUCtUr81 steal in gr~~ral building construction ( revfacd ).

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I§:806 -1968

in general. It would, therefore, be recognized that large scale use of tubular steel in structural work is of considerable importance in the interest of steel economy.

0.5 In order to popularize the use of tubular construction, it is also proposed to compile design handbooks, typical designs and other aids to design which, when they become available, would be of assistance to those not previously experienced in tubular design and construction. 0.6 Grades YSt 22, YSt 25 and YSt 32 of steel tubes mentioned in this standard are covered in IS : 1161-1963*.

0.7 In the formulation of this code, assistance has been derived from B.S. 449 : 1959 ‘ Use of structul.al steel in building’, issued by the British Standards Institution.

0.8 This standard contains clause 7.8 which calls for agreement between the purchaser and the manufacturer.

0.9 For the purpose of deciding whether a particular requirement of this standard is complied with, the final value, observed or calculated, ex- pressing the result of a test or analysis, shall be rounded offin accordance with IS : 2-1962t. The number of significant places retained in the rounded off value should be the same as that of the specified value in I this standard.

1. SCOPE

1.1 This code deals with the use of structural steel tubes in general building construction and is complementary to IS : 800-19621. Provisions which are of special application to construction using steel tubes are included in this code.

2. GENERAL

2.1 Unless otherwise specified in this code, provisions of IS : 8OO-1962$ with regard to terminology, plans and c’rawings, loads and general consi- derations for the design, fabrication and erection are applicable in the use of steel tubes in general building construction.

3. MATERIALS

3.1 Steel Tubes --Steel tubes used in building construction shall be hot finished tubes conforming to the requirements specified in IS : 1161-

1963*

*Specification for steel tubes for structural purposes (revised) ( Second revision in 1968 ).

tRules for rounding off nulnerical values ( revised).

$Code of practice for we of structural ateel in general building construction ( revised ).

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Is:806-

196%

3.1.1 Tubes made by other than hot finishing processes, or which have been subjected to cold working, shall be regarded as hot finished if they have subsequently been heat-treated and are supplied in the normalized conditions.

NOTE - Grade EltW YSt 22 tubes specified in IS : 1161-1963’ with a carbon content less tb~n 0.30 percent, may be considered as hot finished for the purposes of 3.1.1.

3.2 Electrodes -The electrodes used for welding steel tubes shall con- form to the requirements of IS : 814-19631_.

4. WIND PRESSURE

4.1 In calculating the effective wind pressure on exposed circular tube members of a structure, the effective area shall be taken as 0.6 times the projected area of the member. ( Refer to IS : 875-1964$ for values of wind pressure. )

5. PERMISSIBLE STRESSES

5.0 The provision as regards permissiblestresses on the net or gross cross- sectional areas, as the case may be, in 5.1 to 5.8 of this code, is applica- able to steel tubes for which the minus tolerance on the weight per unit length of tube is not more than 4 percent. If on the steel tubes used the minus tolerances on the weight per unit length are larger than 4 percent, a corresponding reduction in cross-sectional areas is required to be made in applying the permissible stresses.

5.1 Axial Stress in Tension -The direct stress in axial tension on the net cross-sectional area of tubes shall not exceed the values of F1 given in Table 1.

TABLE 1 PERMISSIBLE AXIAL STRESS IN TENSION

GRADE (1) Yst 22 Yst 25 Yst 32 FI (2) kgf/cm’ 1250 1500 1900

5.2 Axial Stress in Compression - The direct stress in compression on the cross-sectional area of axially loaded steel tubes shall not exceed the values of F, given in Table 2 in which l/r is equal to the effective length of the member diviclrd by the radius of gyration.

*Specific&tion for steel tubes for structural purposes ( revised ) (Second revision

in 1968 ).

tSpecificetion for covered electrodes for metal arc welding of mild steel ( revised) ( Third revision in 1979 ).

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_.

Is:806-1968

TABLE 2 PERMISSIBLE AXIAL STRESS IN COMPRESSION ( Clause 5.2 )

I/r FC

C__--_--__--h----___---5

GBADE YSt 22 GRADE YSt 25 GRADE YSt 32

kgf/cm* kgf/cm’ kgf/cm* (1) (2) (3) (4) 0 1 260 1 boo 1 900 LO 1217 1448 1 821 20 1175 1400

i

760 30 1131 I 352 1 G79 4a 1088 1 303 1610 50 1046 1 255 1539 60 1002 1 207 1 468 70 970 1 155 1375 80 929 1088 1 263 90 876 1003 1 128 too 814 910 989 110 745 813 869 120 674 721 758 130 603 638 665 140 WO b6b 684 lb0 490 503 517 160 432 443 450 170 381 392 398 I80 339 348 353 190 304 311 316 200 271 278 280 210 243 249 250 220 219 225 227 230 198 204 208 240 180 185 187 2bo 162 167 167 300 106 106 106 350 71 71 72

NOTE I -Intermediate values may be obtained by linear interpolation.

NOTE 2 -The formula, from which these values have been derived, is given in Appendix A.

5.3 Bending Stresses- In tubes, the tensile bending stress and the compressive bending stress in the extreme fibres shall not exceed .the values ,of Fb given in Table 3.

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IS

:806-1968

TABLE 3 PER\IISSIBLE BENDING STRESS IN EXTREME FIBRES 1N

TENSION AND COMPRESSION ( C/a,tsr, 5.3 1 GRADF. FII (1) (2) kgf,rm* YSt 22 1400 Yst 25 1 655 YSt 32 2 050

5.4 Shear Stress - The maximum shear stress in a tube calculated by dividing the total shear by an area equal to half the net cross-sectional area of the tube shall not exceed the values of

F,

given in Table 4. The net cross-sectional area shall be derived by deducting areas of all holes from the gross cross-sectional area.

TABLE 4 PERMISSIBLE MAXIMUM SHEAR STRESS GRADE (1) Yst 22 YYt “3 YSt 32 F, (2) kgf/cm’ 900 1 100 1350

5.5 Bearing Stress -The average bearing stress on the net projected area

of

contact shall not exceed the values of

Fn

given in Table 5.

TABLE 5 PERMISSIBLE MAXIMUM BEARlNG STRESS

GRADE (I! \-St 22 YSt 25 \‘st 32 FP (2) kgf/cm’ 1 700 I 900 2 500

5.6 Combined Bending and Axial Stresses - Members subject to both bending and axial stresses shall be so proportioned that the quantity:

where

.I;, = calculated axial stress, that is, asial load divided 1,) appropriate area 01‘ member;

Fa - pernlissible stress in member for axial load;

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tS:806-1968

.fb

= calculated bending stress in the extreme fibre; and Fb = permissible bending stress in the extreme fibre.

5.6.1 When bending occurs about both axes of the member, fb shall be taken as:

f, = t’(f*+ l2 + (/bY 1”

where fiz and/,, dI’e the two calculated unit fibre stresses.

5.7 Permissible Stresses in Welds

5.7.1 Butt IVe!ds --The stress itI a butt weld shall be calculated on an area equal to the effective throat thickness multiplied by the effective length of the weld measured at the centre of its thickness. In a butt weld the allowable RJlSiie, compressive and shear stresses shall not exceed the stresses respectively permissible in YSt 25 tubes or in the parent metal, whichever is less.

5.7.2 Fillet Welds and Filiet-Burt Welds - 1 see 6.7.3.2(cj j -- The stress in a fillet weld or a fillet-butt weld shall be calculated OJI an area equal to the minimum effective throat thickness multiplied by the length of the weld. A method of calculating the length of the weld is given in Appendix EL In a fillet weld or in a tillet-butt weld, the permissible stress shall not exceed the shear stress permissible in YSt 25 tubes or in the parent metal, whichever is less.

5.7.2.1 Conlbined stresses in afillet orfiller-butt weld - LVhcn the fillet welds in a connection arc subjected to the action of bending combined with direct load, the maximum resultant stress shall be calculated as the vector sum, and shall not exceed the permissible stress as specified in 5.7.2.

5.8 Increase of Stresses

5.8.1 Increase of permissible stresses ~OJ occasional loads may be allowed according to the provisions of IS : 800-1962*

5.8.2 Irrespective of any permissible increase of allowable stress,.the equivalent stress,f, due to co-existent bending and shear stresses shall not exceed the values given in Table 6.

TABLE 6 MAXIMUM ALLOWABLE EQUIVALENT STRESS

GRADE F, (1) (2) kgf/cm’ Yst 22 19oc k’st 25 2 285 YSt 32 2 no0 ---_-

*Coda of practice for use cl’ structu ral steel in general building construction ( revised ).

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IS:806-1968 5.8.2.1 The equivalent stress

f,

is obtained from the following formila:

f r. = &? + 3Ja where

fb = the calculated bending stresses ( compression or tension ) at the point under consideration, and

fs =

the calculated actual co-existent shear stress at the point under consideration.

6. DESIGN

6.1 General -The principles and procedures of design contained in Section IV of IS : 80%1962* generally applicable to structures using steel tubes.

6.2 Basis of Design -The basic methods of design for structures using steel tubes are generally similar to those for other types of elastic structures. Welding is generally adopted for connections in tubular steel construction. Since the connections in such cases give rigid joints, it is desirable to design such welded structures taking into consideration the actual condition of rigidity particularly since such design results in saving in materials and greater overall economy. For structures designed on the basis of fixity of connections, full account is to be taken ofthe effects of such fixity.

6.2.1 Structural frameworks using steel tubes including those with welded connections may, however, be designed on a simple design basis, comparable with that given in IS : 800-1962*. In such cases, secondary stresses may be neglected in the design of trussed girders or roof trusses, except where the axes of the members do not meet at a point. Where there is such eccentricity, the effects of the eccentricity should also be considered.

6.2.2 Curved Members and Bends -The design of curved members and bends shall be given special consideration, alld allowance shall be made for any thinning of the bent pal t which may be caused by bending the member.

6.3 Minimum Thickness of Metals

6.3.1 For tubular steelwork painted with one priming coat of red oxidezinc chromate paint after fabrication and periodically painted and maintained regularly, wall thickness of tubes used for construction exposed to weather shall be not less than 4 mm, and for construction not exposed to weather it shall be not less than 3.2 mm; where stiuctures are not readily accessible for maintenance, the minimum thickness shall be 5 mm.

*Code of practice for use of structural eteel in general building construction

( revised 1.

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15:806-1968

6.3.2 Steel tubes used for construction exposed to weather shall be not less than 3.2 mm thick and for construction not exposed to weather shall be not less than 2.6 mm thick, provided in each case the tube is applied with:

a) one coat of zinc primer conforming to IS : 104-1962* followed by a coat of paint conforming to IS : 2074-1962t, and

bj two coats of paint conforming to IS : 123-19622.

This painting sysfem should be renewed after every two years in the case of tubes exposed to weather. In case some other metallic corrosion protecting material is used, such as aluminium painting, the renewal of coating may be done after longer intervals.

6.4 Compression Members

6.4.1 Eflective Length of Compression Members - Effective length (I) of a compression member for the purpose of determining allowable axial stresses shall be assumed in accordance with Table 7, where L is the actual length of the strut, measured between the centres of lateral supports. In the case of a compression member provided with a cap or base, the point of lateral support at the end shall be assumed to be in the plane of the top of the cap or bottom of the base.

TABLE 7 EFFECTIVE LENGTH OF COMPRESSION MEMBERS

TYPE EFFECTIVF: LRNGTH

Effectively held in position and restrained in dmxtion trt 0.67 L

both ends

Effectively held in position 8t both ends and restrained in

direction at one end ws5 L

Effectively held in posit.ion at. both ends but not restrained in

direction L

Effectively held in position and restrained in direction at one

end, and at the other end effectively restrained in direction but not held in position

L

Effectively held in position and restrained in direction at one end, and at the other end partially restrained in’ direction but not held in position

1.5 L Effectively held in position and restrained in direction at one

end but not held in position or restrained in direction at t.he other end

2.0 L

*Specification for ready mixed paint, brushing, zinc chrome, priming, for use on aluminium and light alloys ( revised ).

tspecilicstion for ready mixed paint, red oxide-zinc chrome, priming.

~+ecification for ready mixed paint, brushing finishing, semi-gloss, for genCral R urposea, to Indian Standard colours No. 445 Venetian red, No448 Deap Indian red, O. 451 Chocolate, No. 446 Red oxide, No. 449 Light purple brawn, No. 473 Gulf red and red oxide (colour unspecified ) ( revised 1.

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6.4.1.1 Mhnbers of trusses - In the case of bolted, riveted or

weldtd trusses and braced frames, the effective length (r) of the camp-

rtssion*mtmbers shall be taken as between O-7 and 1-O times the distance between ctntres of intetsectlons, depending on the degree of end rts- traint provided.

6.4.2 Maximum .Slmderness Ratio of Compression Members - The ratio of effective length (I) to the appropriate radius of yration (t) of a compression member shall not exceed the following va ues: f

4 b)

4

Type of Member

Carrying loads resulting from dead loads and superim- posed loads

llr

180 Carrying loads resulting from wind or seismic forces only,

provided tht deformation of such members doej not ad- versely, affect the stress in any part of the structure Normally acting as a tie in a roof truss but subject to possible reversal of stress resulting from the action of wind

250

350

6.4.3 Eccentricity of Beam Reactions on Columns - For the purpose of determining the eccentricity of beam reactions or similar loadi on a column in simple design procedure, the load shall be assumed to be applied as given in Table 8.

8x4 No. 0) i) ii) i ii ) iv)

TABLE 8 ASSUMED BCCENTMCITY OF i&MD@ IN COUlMNS

TYPO OF CONNICTION AUBUBIBD Poem or AP?LICATSOBI

(2) @I

Stiffened bracket Uncltiffened bracket Clesta on tube

cap:

Mid-point of stiffened seating Outer face of vertical leg of bracket Out&de of tube

a) Beams of approximntely bqual rpan and load, continuour over the cap

Mid-point of cap

b) Other beams c) Roof truss beerings

Edge of atencbion torarb rpem of beam except for roof truss bearings

No eccentricity for simple bearing without connections capable of davel9ping an apprecrable moment

6.44 Joints

6.4.4.1 Where in joints in compression members, the ends of the

members are faced for bearing over their whole area, the welding and joining material shall be suffkient to retain the members accurately in

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E8:886-1968

place and to resist all forces other than direct compression, including those arising during transit, unloading and erection:

6.4.4.2 Where such members are not faced for complete bearing, the welding and joining material shall be sufficient to transmit all the forces to which the joint is subjected.

6.4.4.3 Wherever possible, joints shall be proportioned and ar- ranged so that gravity axes of the members and the joints are in line, so as to avoid eccentricity. 6.4.5

Column Bases

6.4.5.1

Gusseted bases

a)

b)

4

For columns with gusseted bases the gussets and the welds con- necting them to the shaft shall be designed to carry the load and bending moment transmitted to them by the base plate; Where the end of the column shaft and tbe gusset plates are faced for bearing over their whole area, the welds connecting them to the base plate should be sufficient to retain the parts securely in place and to resist all forces other than direct compression, including those arising during transit, unloading and erection.

Where the end of the column shaft and the gusset plates are not faced for complete bearing, the welds connecting them to the base plate shall be sufficient to transmit all the forces to which the base is subjected.

6.4.5.2

Slab bases -

For columns with slab bases where the end of

the shaft is faced for bearing over its whole area, the welds connecting it to the base plate should be sufficient to retain the parts in place and

to resist all forces other than direct compression including those arising .during transit, unloading and erection.

see 19.8.2 of IS : 800-1962*. ) ( Fdr the design of slab bases 6.4.6

Latticing and Battening of Compression Members

6.4.6.1

Latticing and battening where necessary shall be propor-

tioned according to the appropriate clauses of IS : 800-1962*.

6.4.6.2 Whenever possible, lattices and battens shall be so arrang- ed that their gravity axes are in line with gravity axes of the main members to which they are connected.

6.5 Dasiga

of Berms

6.5.1

The tensile and compressive stresses in the extreme fibrcr of tubes in bending shall not exceed the values prescribed under 5.3.

*cod0 Of prWtiC0 for U66 Of 6trUChld 6bd in gdnmal building cOn6t~otiOU ( rrvkd L

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IS:806-1968

6.5.2

The maximum shear stress in tubes in flexure, calculated by

dividing the total shear by an area equal to half to the net cross-sectional area of the tube, shall not exceed the values prescribed under 5.4.

6.5.3 Stifleners for Tubes - Where the tubular steel beam rests on abutment or other supporting member, it shall be provided with a shoe adequate to transmit the load to the abutment and to stiffen the end of the tube.

6.5.3.1 Where a concentrated load is applied to a tubular member transverse to its length or the effect of load concentration is given by the intersection of triangular truss members, consideration shall be given to the local stresses set up and the method of application of the load, and stiffening shall be provided as necessary to prevent the local stresses from being excessive. The increase in the intensity of local bending stresses caused by concentrated loads is particularly marked if either the diameter of connected member or the connected length of a gusset or the like is small in relation to the diameter of the tubular member to which it is connected.

6.5.4 Limiting Dejections of Beams - The deflection of a member

shall not be such as to impair the strength, efficiency or appearance of the structure or lead to damage to fittings and finishings. Generally, the maximum deffection should not exceed l/325 of the span for sim supported members. Th is requirement may be deemed to be satis g cd ly if the bending stress in compression or tension does not exceed

315OOD -

I kgf/cm4, where D is the outer diameter of the tube in cm and I is the effective length of the beam in cm.

6.5.4.1 Purlins

a) The requirements uuder 6.5.4 regarding lixniting deflection may be waived in the design of simple tubular purlins provided that the following requirements are satisfied:

NATURE OF .END MINIMUM VALUE OF SECTION MINIMUV~

FIXING MODULUS &lTSIDE

C--- h---__._ - __~ DIAMETER

Grade Grade Grade FOR GRADES

YSt 22 YSt 25 YSt 72 sst 22.

cm3 (.m:, cm3 YSt 25

AND YSt 32 cm Simply supported WL/ 11200 lVL/ 13 230 WL/ 16 400

Effectively continuous WLI 16 800 WLI 19 840 WL124.600 :I$:

where

W- the total distributed load in kg on the purlins arising

from dead load and snow but excluding wind, and 13

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lS:806-1968

L. =

the distance in cm between the centres of the steel princi- pals or other supports.

b) A purlin shall be considered as effectively continuous at any intermediate point of support if it is actually continuous over that point or if it has there a joint able to provide a fixing moment of not less than WL/l2, where

W

and

L

are as defined above.

6.6

Separators and Diaphragms -

When loads are required to be carried from one tube to another or are required to be distributed between tubes, diaphragms which may be tubular, designed with suffi-

cient stiffness to distribute the load between the tubes, shall be used. 6.7 Connections

6.7.1 General-Connections in structures using steel tubes shall be provided by welding, riveting or bolting. Wherever possible, coanec- tions between tubes shall be made directly tube to tube without gusset plates and other attachments. Ends oftubes may be Battened as specified in 7.7 or otherwise formed to provide for welded, riveted or bolted connections.

6.7.2

Eccentricity

qf

Members -Tubes

meeting at a point rhall, wherever practicable, have their gravity axes meeting at a point SO

as

to avoid eccentricity.

6.7.2.1

Eccentricity

of

connections -

Wherever practicable, the centre of resistance of the connection shall lie on the line of action of the load so as to avoid eccentricity moment of the connection.

6.7.3

Welded Connections

6.7.3.1

A weld connecting two tubes end to end shall be full penetration butt weld. The eifective throat thickness ofthe weld shall be taken as the thickness of the thinner part joined.

6.7.3.2 A weld connecting the end of one tube ( branch

tube) to

the surface of another tube ( main tube ) with their axes at an angle of not less than 30” shall be of the following types:

a) A butt weld throughout, b) A fillet weld throughout, and

c) A fillet-butt weld, the weld being a fillet weld in one part and a butt weld in another with a continuous change from the one form to the other in the intervening portions.

Type (a) may be used whatever the ratio of the diameters of the tubes joined, provided complete penetration is secured either by the use of backing material, or by depositing a sealing run of metal on the back of the joint, or by some special method of welding. When type (a) is not employed type (b) should be used where the diameter of the branch tube is less than one-third of the diameter of the main t&e, and

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IS:806-1968 type (c) should be used where the diameter of rhe branch tube is equal to or greater than one-third of the diameter of the main tube.

For the purpose of stress calculation, the throat thickness of the butt weld portion shall be taken as the thickness oi the thinner pax,t joined, and the throat thickness of the fillet weld and the fillet-butt weld shall be taken as the minimum effective throat thickness of the fillel o fillet- butt weld.

6.7.3.3 Angle between tubes - f\ weid connecting the end of one tube to the surface oranother, with the axes of the tubes intel,secting at an angle of less than 30”, shall be permitted only if adequate efficient) of the junction has been demonstrated.

6.7.3.4 Connections where Ihe axes ofthe two tubesdo not irftersecf -. A weld connecting the end of one tube to the surface of another whelc the axes of the two tubes do nor intersect, shall be subject to the provisions under 5.7, 6.7.3.2 and 6.7.3.3, provided that no part of the curve ofintersection of the eccentric tube with the main tube lies outside the curve of intersection of the corresponding largest permissible non- eccentric tube with the main tube (see Fig. I ).

6.7.3.5 Connections of tubes with flatterred ends -Where the end of the branch tube is flattened to an elliptical shape 5.7, 6.7.3.2 to 6.7.3.4 shall apply, and for the application of 6.7.3.2 and 6.7.3.4 the diameter of the flattened tube shall be measured in a plane perpendicular to the axis of the main tube.

7. FABRKATION 7.1 General

7.1.1 The general provisions in Section V of IS : 800-i962* are also applicable to the fabrication of structures using steel tubes. Where welding is adopted, reference to appropriate provision of IS : 820- t

{Ire Note ) and IS : 816-1956$ shall be made.

NOTE -Until this standard is published, provisions for welding in tubular construction shall be as agreed to between the concerned parties.

7.1.2 The component parts of the structure shall be assembled in such a manner that they are neither twisted nor otherwise demaged and be so prepared that the specified cambers, if any, are maintained.

*Code of pract: .e for use of structural stoel in general building cmstruction ( revised ) .

tCode of practice for use of r;elding in tubukr construction (undzr prepurafion ). fCo& of practice for use of metal are \velding

steel. ( Since revised ). for general construction in mild

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IS : 806 - 1968

TYPE I Butt Weld ema. = + (9, - De,)

TYPE It Fillet Weld

e

. \

//

. \

e

--I- - --- -

l!L?Pl

-t .-+-- -f t

--

L-

--$

aE

\

\ --‘--- 2-L

/

TYPE III Fillet-Butt Weld e mar =+(k0,)

e,h = +(!$ -0~)

NOTE - Dotted circle shows curve of intersection of largeet permicMibb non- eccentric tube with main. Solid circle indicates curve of intersection of ecosntric branch.

FIG. 1 DIAGRAM SHOWING LIMITS OF ECCENTRICITY FOR TUBE CONNECTIONS

7.2 Straightening-All material before being assembled shall be straightened, if necessary, unless required to be of a curvilinear form

and shall be free from twist.

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lS:806-1968

7.3 Bolting

7.3.1

Washers shall be specially shaped where necessary, or other means used, to give the nuts and the heads of bolts a satisfactory bearing.

7.3.2 In all cases where the full bearing area of the bolt is to be developed, the threaded portion of the bolt shall not be within the thickness of the parts bolted together, and washers of appropriate thickness shall be provided to allow the nut to be completely tightened. 7.4

Cut Edges -

Edges should be dressed to a neat and workmanlike finish and be free from distortion where parts are to be in contact metal-to-metal.

7.5

Caps and Bases for Columns -

The ends of all tubes for columns, transmitting loads through the ends, should be true and square to the axis of the tube and should be provided with a cap or base accurately fitted to the end of the tube and screwed, welded or shrunk on.

7.5.1 The cap or base plate should be true and square to the axis of the column.

7.6

Sealing of Tubes -

When the end of a tube is not automatically sealed by virtue of its connection by welding to another member, the end shall be properly and completely sealed.

7.6.1 Before sealing, the inside of the tube should be dry and free from loose scale.

7.7 Flattened

Ends -

In tubular construction, the ends of tubes may be flattened or otherwise formed to provide for welded, riveted or bolted connections provided that the methods adopted for such 0attening do not injure the material. The change of section shall be gradual. 7.8

Oiling and Painting -

If not galvanized, all tubes shall, unless otherwise specified, be painted or oiled or otherwise protectively coated before exposure to the weather. If they are to be painted in accordance.with any special requirements, this shall be arranged between the purchaser and the manufacturer.

7.9 Marking,

Shop Eiection and Packiog -

Appropriate provisions of IS : 800-1962* shall apply.

8.

INSPECTION AND TESTING

8.1

Appropriate provisions of IS : 800-1962* shall apply.

*Code of practice for use of struct,urnl steel in general building comtruetion ( revised ).

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IS:

806-1968

APPENDIX

A

(

Table

2,

Note

2 )

FORMULA FOR DERIVING PERMISSIBLE AXIAL STRESS IN COMPRESSION

A-l. For values of l/r less than 60, the value of F, shall not exceed that obtained from linear interpolation between the value of F, for l/r = 60 as found under A-2 and a value of 0.6f, for l/r z 0.

A-2. For values of f/r from 60 to 150, the average axial stress on the cross-sectional area of a strut or other compression member shall not exceed the value of F, obtained by the formula given below:

I

F, z--1

I + 0.15 set ( t;$F) radians

where

F, = the permissible average axial compressive stress;

fu =

the guaranteed minimum yield stress;

nr = factor of safety taken as l-67;

i/r = slenderness ratio, ‘I’ being the effective length and ‘r’ radius of gyration; and

E = modulus of elasticity 2 047 000 kgf/cms.

A-3. For values of l/r greater than 150, the average axial stress on the cross-sectional are? of a strut or other compression member shall not 1 exceed the value Fe ( 1.2 - T&-r ) where F, is obtained as given under A-2.

APPENDIX

B

(

Clause

5.7.2 )

DETERMINATION OF THE LENGTH OF THE CURVE OF INTERSECTlON OF A TUBE WITH ANOTHER TUBE

OR WITH A FLAT PLATE

B-l. The length of the curve of intersection _{-_} (see Fig. 2) may be taken as: _{_} P = a -I- b f 3,“~” + b2

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IS:806

-1%8

where d a = -;; cosec fj; L d

b=-x ₃ _2-3 - (d/D )” _(d/D)a for intersection with a tube (see Note)

= -$, for intersection with a flat plate;

d = outside diameter of branch;

6 = angle between branch and main; and

D = outside diameter of main.

NOTE - Alternatively, b = +> where 0 is measured in radianr and

# Ii rin - = - .

2 D

FIO. 2 LENOTH OF THE CURVEOF INTERSECTION OF A TSJEE WITH ANOTHER TUBE OR wlrH A FLAT PLATE

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